The present invention relates to an apparatus for and a method of extracting samples of product from process lines, pipes or vessels. More particularly, the invention relates to an apparatus for and a method of extracting samples of a fluidized product, such as wood pulp slurry, in which strands, viscous strings and discrete particles may be entrained.
Certain manufacturing operations require that the immediate or overall composition of a liquid or fluid product flowing through a process line or contained within a vessel or tank be monitored. Such monitoring ordinarily is accomplished with sampling apparatus that takes samples of product from a main body of the product. Where a composite sample is required, the sampler may be periodically operated to withdraw a series of samples of a measured volume of product passing a sampling point. The individual samples are collected and admixed to form a composite representative of the total volume of product.
Other uses for samplers are in on-line analysis applications, in which the immediate composition of a product must be determined. For this application, the individual samples are analyzed separately.
With some other types of samplers, product flows into an opening in a probe and is then removed, for example by being conveyed through and out of the probe by the pressure of the product in the process line, by being gravitationally conveyed through and out of the probe, or by being collected within the probe for subsequent removal. Such samplers depend for proper operation on the ability of the product to flow into and/or out of the probe, and are not well suited for sampling product that has a tendency to plug up the probe opening or coagulate within the probe.
Another type of sampler continuously diverts a stream of product from a process line, and from the diverted stream samples are removed in various ways. Attempts to withdraw small, measured quantities directly from a line, however, have presented problems not altogether satisfactorily solved. For example, in the case of a sampler comprising a probe that has a receiving hole or slot extended directly into a pipe, the sampler often requires an orienting mechanism, and sampled product can build up in such holes and slots and either block the sampler or contaminate subsequent samples.
With some samplers, discrete samples are removed from a main body of product by extending a sample receiving chamber into, and then extracting the chamber from, product in the process line. Such samplers are usually characterized by a housing having a bore, with one end of the bore in communication with the interior of a product-containing vessel. A plunger is in the bore and has a sample receiving chamber in the form of a recess intermediate its ends. Means are provided for reciprocating the plunger in the bore to project the recess into the vessel to receive a sample of product therein, and to then retract the recess and product sample from the line to a sample collection point in the bore. Seals on the plunger to opposite sides of the recess maintain a seal between the product in the process line and the sample collection point during reciprocation of the plunger. Four exemplary types of such prior samplers are disclosed in U.S. Pat. Nos. 4,147,062, 4,262,533, 4,475,410 and 4,744,255, issued to Ben E. Jaeger, the present inventor and teachings of which patents are incorporated herein by reference. Sampling apparatus of the type disclosed in said patents is attached to a port to a process line or vessel containing the liquid or fluid product to be sampled. This enables a sample chamber in a plunger of the sampler to be extended into the product to receive a product sample in the chamber. The plunger is then retracted to deliver the product sample to the collection point in the sampler.
Conventional samplers of the above type operate satisfactorily with product that is relatively fluent and of generally uniform consistency, but they often are less than satisfactory for sampling fluidized product in which strands, viscous strings and relatively large discrete particles are entrained, such as wood pulp slurry containing knots. It is difficult for a conventional sampler to convey such product to a collection point within the sampler, since the particulate material in the product can block openings in the sampler and otherwise interfere with movement and proper operation of the sampler.
A prior sampler that is adapted to sample fluidized product containing relatively large particulate material is disclosed in U.S. Pat. No. 5,585,576, issued to Ben E. Jaeger, the present inventor and the teachings of which are incorporated herein by reference. The sampler of said patent has a housing with a bore that communicates at one end with the interior of a process line or vessel containing fluidized product. A plunger assembly in the bore has a sample chamber intermediate its ends and is reciprocated to project the sample chamber out of the bore and into the vessel to receive a sample of product therein, and to then retract the sample chamber from the vessel and into the bore to a sample collection point. A rearward facing cutter on the plunger, at a forward end of the sample chamber, cooperates with the housing at the one end of the bore, upon retraction of the plunger, to slice through any particulate matter that may be extending partially out of the sample chamber and that would otherwise interfere with retraction of the plunger into the bore. Forward and rearward plunger seals on opposite sides of the sample chamber always maintain a liquid seal between the one end of the bore and the sample collection point. The rearward seal comprises a shear bearing having a circumferential groove that receives and retains fluidized product in sealing relation to the bore to seal the shear bearing and thereby the plunger assembly to the bore. The product collection point in the bore includes a plurality of passages in the housing that communicate with the bore and are sized to prevent passage therethrough of relatively large product particles. Upon reciprocation of the plunger assembly to project the sample chamber into the vessel, the shear bearing cuts off and conveys back into the vessel any pieces of product that may have become caught in the passages during the previous sampling cycle and that extend into the bore.
While samplers constructed according to said U.S. Pat. No. 5,585,576 have been successfully used to sample fluidized fibrous product such as wood pulp, depending upon the nature of the product and its flow velocity, extending the forward end of the plunger into the product flow can sometimes result in destruction of the plunger. This can occur because the sample chamber of the plunger is annular in shape and defined around a relatively small diameter stem that connects the plunger forward end to the plunger rearward end. Because it has a relatively small diameter, the resistance of the stem to longitudinal bending is relatively limited. Should the product being sampled have a flow velocity that is unusually high and turbulent, when the plunger is extended into the product flow to obtain a sample, the force exerted by the product on the plunger forward end can bend the stem longitudinally and destroy the plunger. Even if the stem is not bent enough to destroy the plunger, limited bending can result in the rearward facing cutter at the front of the sample chamber being impacted against the housing at the front end of the housing bore upon retraction of the plunger, which can severely damage the cutter and housing.